The invention relates generally to the copying of originals, e.g., photographic originals.
More particularly, the invention relates to a method of, as well as an arrangement and a copy material for, reproducing an original point-by-point.
It is known to form a photographic image of an original on light-sensitive material point-by-point using a light beam. The transparency of the original is measured at different points, and the transparency values are used to control the intensity of the beam. The transparency values may be temporarily stored after measurement of the original and retrieved from storage when the original is to be reproduced.
Several variations of the copying procedure outlined above have been proposed. This procedure is of interest because point-by-point exposure of the copy material makes it possible to change the density range of an original in dependence upon the sensitivity of the copy material. As a rule, the density range of an original is reduced in order to conform to the sensitivity of the copy material. Furthermore, the preceding copying procedure enables so-called image improvement such as, for example, an increase in the definition of edges, to be achieved.
In spite of its benefits, the above copying procedure has not been accepted commercially because the improvement in subjective image quality is not sufficient to warrant the additional cost. Based on earlier research, subjective image quality is represented essentially by the sharpness of the image which, in turn, is best represented by the modulation transfer function. See, for instance, the article "Ermittlung des Zusammenhanges zwischen der subjektiven Gute und den physikalischen Eigenschaften des photographischen Bildes", Biedermann, Klaus; Photographische Korrespondenz, Vol. 103, pp. 5-14, 26-31 and 42-48. However, the modulation transfer function of an image produced electronically point-by-point using a cathode ray tube, for example, as an imaging element does not, as long as the number of points is small enough for economical operation, yield an image significantly better than one of similar resolution produced via a conventional integral exposure. The reason is that the beam from a cathode ray tube has an approximately Gaussian intensity distribution so that such a beam is unable to precisely reproduce an infinitely sharp black-to-white transition in an original.